Software controlled electronic dimming ballast

ABSTRACT

A software controlled electronic dimming ballast for preheating, striking, and varying the dimming level of a lamp. In one embodiment, the ballast includes an EMI filter circuit, an AC/DC converter circuit, a PFC circuit, an inverter circuit, and a software controlled microcontroller circuit. The microcontroller circuit includes a microcontroller and software for generating inverter control signals that cause the inverter circuit to preheat, strike, and varying the dimming level of the lamp. The inverter control signals are generated based on dimming control and lamp dimming level feedback signals. The ballast also includes a lamp dimming level feedback signal conditioning circuit for generating the lamp dimming level feedback signals. Alternative embodiments of the ballast are also described.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 10/726,018 filed Dec. 2, 2003, entitled “Software ControlledElectronic Dimming Ballast” and which is now U.S. Pat. No. 7,443,113.

A portion of the disclosure of this patent document contains materialthat is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and Trademarkoffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO SEQUENCE LISTING OR COMPUTER PROGRAM LISTING APPENDIX

Not Applicable

BACKGROUND OF THE INVENTION

The present invention relates generally to electronic dimming ballastsfor gas discharge lamps.

More particularly, this invention pertains to a software controlledelectronic dimming ballast.

Electronic dimming ballasts are well known in the art. These ballastsare typically designed to be connected to and receive power from analternating current (AC) power source and to be connected to and supplyAC power to a lamp load including one or more gas discharge lamps. Tofacilitate this function, prior art ballasts usually include analternating current/direct current (AC/DC) converter circuit 14 and aninverter circuit 18. The AC/DC converter circuit 14 converts lowfrequency AC voltage supplied by the AC power source into DC voltage andthe inverter circuit 18 converts the DC voltage supplied by the AC/DCconverter circuit 14 into high frequency AC voltage. In someapplications, prior art ballasts may also include an electromagneticinterference (EMI) filter circuit, which is used to filter out noise inthe ballast, and a power factor control circuit that is used to ensurethat the power factor associated with the ballast stays at a desiredlevel.

As the name suggests, electronic dimming ballasts are also designed sothat they can be used to dim the light output of the lamp load connectedto one of these ballasts. To facilitate this function, electronicdimming ballasts usually include some type of dimming control circuitthat can be used to decrease and increase the light output of the lampload. The dimming control circuit usually accomplishes this function bysimply decreasing and increasing the power supplied by the invertercircuit 18 to the lamp load.

An example of a prior art electronic dimming ballast manufactured andsold by the assignee of the present invention, Universal LightingTechnologies, is shown in FIG. 1. This electronic dimming ballast isdesigned to be connected to and receive low frequency AC voltage from anAC power source and to supply high frequency AC voltage to a lampincluding one or more gas discharge lamps. The ballast includes an EMIfilter circuit, an AC/DC converter circuit, a PFC circuit, an invertercircuit, and a dimming control circuit.

The dimming control circuit includes a dimming control signalconditioning circuit, a microcontroller circuit, a pulse width modulator(PWM) circuit, and a lamp current sensing circuit. The dimming controlsignal conditioning circuit is used to receive a dimming control signalfrom an appropriate dimming control device and to generate a conditioneddimming control signal that can be applied to the microcontrollercircuit. The microcontroller circuit is designed to generate amicrocontroller dimming control signal based on the conditioned dimmingcontrol signal and to supply that signal to the PWM circuit. The lampcurrent sensing circuit is designed to receive a lamp current signalfrom the lamp load, to generate a lamp voltage signal based on thatcurrent signal, and to supply that voltage signal to the PWM circuit.

The PWM circuit uses the microcontroller dimming control signal and thelamp voltage signal to generate and supply a pulse width modulatedinverter dimming control signal to the inverter circuit in the ballast.More specifically, the PWM circuit generates an error signal bycomparing the microcontroller dimming control signal and the lampvoltage signal using a differential amplifier and uses that error signalto generate the appropriate pulse width modulated inverter dimmingcontrol signal. By varying the pulse width of the inverter dimmingcontrol signal, the dimming control circuit can vary the power suppliedby the inverter circuit to the lamp and, as a result, can control thelamp load light output.

Although the electronic dimming ballast shown in FIG. 1 does allow oneto control the dimming level of the lamp load, it has severaldisadvantages. First, the dimming control circuit in this ballastrequires a relatively high number of electronic components, i.e., thedimming control signal conditioning circuit, the microcontrollercircuit, the PWM circuit, and the lamp current sensing circuit, andtakes up a large amount of space in the ballast. This increases the sizeof the ballast and makes it undesirable in applications where availablespace is limited. Second, the high number of electronic componentsincreases the overall cost of the ballast and makes it unsuitable forcertain applications.

What is needed, then, is an electronic dimming ballast that requiresfewer components, is smaller, and is less expensive than the electronicdimming ballast discussed above, as well as other prior art electronicdimming ballasts suffering from similar problems.

SUMMARY OF THE INVENTION

Accordingly, one object of the present invention is to provide anelectronic dimming ballast that includes fewer electronic componentsthan prior art electronic dimming ballasts.

A second object is to provide an electronic dimming ballast that issmaller than prior art electronic dimming ballasts.

Another object of the present invention is to provide an electronicdimming ballast that is less expensive than prior art electronic dimmingballasts.

A fourth object is to provide a dimming control circuit for anelectronic dimming ballast that includes fewer electronic components andtakes up less space in an electronic dimming ballast than prior artdimming control circuits.

Another object of the present invention is to provide an electronicdimming ballast that does not require the use of a PWM chip and itsassociated circuitry.

These objects, and other objects that will become apparent to oneskilled in the art, are satisfied by the software controlled electronicdimming ballast (the “software dimming ballast”) of the presentinvention. In one embodiment, the software dimming ballast of thepresent invention includes an EMI filter circuit, an AC/DC convertercircuit, a PFC circuit, an inverter circuit, a lamp dimming levelfeedback signal conditioning circuit, and a software controlledmicrocontroller circuit. The EMI filter circuit is designed to receivelow frequency AC voltage from an AC power source and to filter noise outof that voltage to generate a filtered low frequency AC voltage. TheAC/DC converter circuit is designed to convert the filtered lowfrequency AC voltage into a rectified AC voltage and to supply thatvoltage to the PFC circuit. The PFC circuit is designed to convert therectified AC voltage into a boosted DC voltage and to ensure that powerdrawn from the AC power source by the software dimming ballast has adesired power factor.

The inverter circuit is designed to receive the boosted DC voltage fromthe PFC circuit and to generate high frequency AC voltages and currentsthat preheat, ignite, and cause the lamp to have a variety of differentlamp dimming levels. The high frequency AC voltages and currents aregenerated by the inverter circuit based on inverter control signalsreceived from the software controlled microcontroller circuit.

The lamp dimming level feedback signal conditioning circuit is designedto sense lamp currents, to generate lamp dimming level feedback signalsbased on the sensed lamp currents, to condition these feedback signalsto generate conditioned feedback signals that can be applied to thesoftware controlled microcontroller circuit, and to supply theseconditioned feedback signals to the software controlled microcontrollercircuit. The conditioned feedback signals are representative of existinglamp dimming levels and the present invention uses these signals todetermine if the lamp is at desired lamp dimming levels.

The software controlled microcontroller circuit is designed to generatethe inverter control signals that cause the inverter circuit to generatethe high frequency AC voltages and currents that preheat, ignite, andcause the lamp to have a variety of different lamp dimming levels. Togenerate these control signals, the software controlled microcontrollercircuit includes a micro controller integrated circuit (IC) that is usedto generate the control signals and control software that causes themicrocontroller IC to generate the control signals. To generate aninverter control signal that causes the inverter circuit to generate anAC voltage and current that preheats the lamp, the control softwarecauses the microcontroller IC to generate a pulse width modulatedinverter control signal having a frequency that is much higher than thenatural resonance frequency of a resonant output circuit included in theinverter circuit. To generate an inverter control signal that causes theinverter circuit to generate an AC voltage and current that ignites thelamp, the control software causes the microcontroller IC to generate apulse width modulated inverter control signal having a frequency that isapproximately equal to the natural resonance frequency of the resonantcircuit. To generate inverter control signal that cause the invertercircuit to generate AC voltages and currents that cause the lamp to havedifferent lamp dimming levels, the microcontroller IC is designed toreceive and convert dimming control signals representative of desiredlamp dimming levels and the conditioned lamp dimming level feedbacksignals representative of existing lamp dimming levels into digitaldata. The control software then uses this digital data to determine ifthe lamp is at desired lamp dimming levels and to generate pulse widthmodulated inverter control signals having varying duty cycles in orderto vary the dimming level of the lamp. Each one of these control signalshas a frequency that is slightly higher than the natural resonancefrequency of the resonant circuit.

The software controlled microcontroller circuit is also designed tomonitor the low frequency AC voltage supplied to the software dimmingballast and to shut down the ballast if that voltage drops too low. Inaddition, the software controlled microcontroller circuit is furtherdesigned to monitor the operating condition of the lamp connected to thesoftware dimming ballast and to shut down the ballast if the lampreaches an end of lamp life fault condition.

The embodiment of the present invention discussed above may vary in anumber of different ways and these variations are described in moredetail in the detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a prior art electronic dimmingballast.

FIG. 2 is a block diagram showing a preferred embodiment of the softwarecontrolled electronic dimming ballast of the present invention.

FIG. 3 is schematic showing a preferred embodiment of the EMI filtercircuit and the AC/DC converter circuit of the present invention.

FIG. 4 is a schematic showing a preferred embodiment of the PFC circuitof the present invention.

FIG. 5 is a schematic showing a preferred embodiment of the voltageregulator circuit of the present invention.

FIG. 6 is a schematic showing a preferred embodiment of the invertercircuit of the present invention.

FIG. 7 is a schematic showing preferred embodiments of themicrocontroller circuit and the lamp dimming level feedback signalconditioning circuit, and portions of the preferred embodiments of thePFC and inverter circuits of the present invention.

FIG. 8 is a schematic showing an enlarged view of the preferredembodiment of the microcontroller circuit and preferred embodiments ofthe line voltage signal conditioning circuit and the blocking capacitorsignal conditioning circuit of the present invention.

FIG. 9 is a schematic showing an enlarged view of the preferredembodiment of the lamp dimming level feedback signal conditioningcircuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 2, a preferred embodiment of the softwarecontrolled electronic dimming ballast 10 (the “software dimming ballast10”) of the present invention includes an electromagnetic interference(EMI) filter circuit 12, an alternating current/direct current (AC/DC)converter circuit 14, a power factor correction (PFC) circuit 16, aninverter circuit 18, a lamp dimming level feedback signal conditioningcircuit 20, and a software controlled microcontroller circuit 22.

The EMI Filter Circuit

The EMI filter circuit 12 includes an EMI input (shown on FIG. 3 asterminals WHT and BLK) so it can be connected to a 120 volt, 60 Hertz(Hz), sinusoidal AC power source 26 (the “AC power source 26”) andreceive low frequency, 60 Hz, sinusoidal AC input voltage (the “AC inputvoltage”) from that source. The EMI filter circuit 12 generates filteredlow frequency sinusoidal AC voltage (the “filtered AC voltage”) byfiltering electromagnetic interference, i.e., noise, out of the voltagesupplied by the AC power source 26 and supplies the filtered AC voltageto the AC/DC converter circuit 14. The filtered AC voltage is suppliedto the AC/DC converter circuit 14 using an EMI output (shown on FIG. 3as terminals 1, 2) included with the EMI filter circuit 12. The EMIfilter circuit 12 also prevents noise generated by the PFC circuit 16and the inverter circuit 18 from passing back into the AC power source26.

As shown in FIG. 3, the EMI filter circuit 12 includes a common modechoke 34, a differential mode line capacitor 36, a differential modechoke 38, a second differential mode line capacitor 40, and two linebypass capacitors, 42 and 44. The common mode choke 34 and the linebypass capacitors, 42 and 44, suppress common mode noise, and thedifferential mode line capacitors, 36 and 40, and choke 38 suppressdifferential mode noise.

The AC/DC Converter Circuit

The AC/DC converter circuit 14 (the “converter circuit 14”) includes aconverter input (terminals 1, 2 on FIG. 3) for receiving the filtered ACvoltage from the EMI filter circuit 12 and a converter output (terminals3, 4 on FIGS. 3 and 4) for supplying a full wave rectified AC voltage(the “rectified AC voltage”) to the PFC circuit 16. The convertercircuit 14 rectifies the filtered AC voltage supplied by the EMI filtercircuit 12 using a full bridge rectifier (not shown).

The PFC Circuit

The PFC circuit 16 causes power drawn from the AC power source 26 by thesoftware dimming ballast 10 to have a power factor ranging fromapproximately 0.95 to 1 and supplies an approximately constant boostedDC voltage (the “boosted DC voltage”) to the inverter circuit 18. Theboosted DC voltage is approximately 450 volts DC. The PFC circuit 16(see FIG. 4) includes a PFC input (terminals 3, 4 on FIG. 4), a PFCinput filter 56, a PFC transistor circuit 58, a PFC control circuit 60,two PFC inductors, 62 and 64, a PFC diode 66, two bulk capacitors, 68and 70, and a PFC output (terminals 5, 6 on FIG. 4).

The PFC input receives the rectified AC voltage from the convertercircuit 14 and the PFC output supplies the boosted DC voltage to theinverter circuit 18. The PFC input filter 56 filters high frequencynoise caused by high frequency switching of the PFC transistor circuit58 and prevents that noise from passing back into the converter circuit14 and the AC power source 26. The PFC control circuit 60 controls thePFC circuit 16 so that it draws a DC current from the converter circuit14 that has a waveform that is approximately the same as the waveform ofthe rectified AC voltage supplied by the converter circuit 14. The PFCcontrol circuit 60 accomplishes this function by periodically switchinga PFC transistor 76 in the PFC transistor circuit 58 off and on, i.e.,by periodically making the PFC transistor 76 nonconductive (off) andconductive (on), and by varying the frequency at which the PFCtransistor 76 is switched off and on. The transistor switching frequencyranges from approximately 10-15 kHz. When the PFC transistor 76 is on,current flows from the converter circuit 14, through the PFC inductors,62 and 64, and through the PFC transistor 76 to ground. When the PFCtransistor 76 is off, energy stored in the PFC inductors, 62 and 64,causes current to flow out of the PFC inductors, 62 and 64, through thePFC diode 66 to the bulk capacitors, 68 and 70. The resulting DC currentcharges the bulk capacitors, 68 and 70, and generates the boosted DCvoltage 52 that is supplied to the inverter circuit 18. The PFC diode 66prevents current from flowing back from the bulk capacitors, 68 and 70,into the PFC circuit 16.

As shown in FIG. 4, the PFC input filter 56 is simply a capacitor 56(the “PFC capacitor 56”). The PFC capacitor 56 is sized so that itpasses the rectified AC voltage generated by the converter circuit 14and blocks higher frequency noise generated by the switching of the PFCtransistor circuit 58. The PFC transistor circuit 58 includes the PFCtransistor 76, a PFC gate resistor 78 for limiting gate current flowinto the gate of the PFC transistor 76, and a PFC gate diode 80 forallowing gate current to flow out of the PFC transistor 76 and bypassthe PFC gate resistor 78.

The PFC control circuit 60 shown in FIG. 4 includes a multiplier inputresistive voltage divider 82 (the “multiplier input divider 82”), asupply voltage resistive voltage divider 84 (the “supply voltage divider84”) connected to a supply voltage input filter 86, an output voltageresistive voltage divider 88 (the “output voltage divider 88”), avoltage feedback compensation network 90 (the “feedback network 90”), azero current detector circuit 92, a current sense resistor 94, and a PFCintegrated circuit (IC) 96 (the “PFC IC 96”). The multiplier inputdivider 82 generates a rectified multiplier input voltage that isproportional to the rectified AC voltage supplied by the convertercircuit 14 and supplies that voltage to a multiplier input pin on thePFC IC 96. The supply voltage divider 84 generates a rectified supplyvoltage that is proportional to the rectified AC voltage supplied by theconverter circuit 14 and the supply voltage input filter 86 filters therectified supply voltage to generate a filtered supply voltage that isan approximately constant DC supply voltage. This voltage is supplied toa PFC supply voltage input pin on the PFC IC 96.

The output voltage divider 88 generates a feedback voltage that isproportional to the boosted DC voltage generated by the PFC circuit 16and supplies that voltage to an inverting input pin on the PFC IC 96.The feedback network 90 is connected to the inverting input pin and acomparator input pin on the PFC IC 96 and ensures that the PFC controlcircuit 60 operates in a stable manner. The zero current detectorcircuit 92 detects when the DC current flowing through the PFC inductorreaches zero, generates a zero current voltage indicative of that fact,and supplies this voltage to a zero current detector input on the PFC IC96. The current sense resistor 94 generates a current sense voltage thatis representative of current flowing through the PFC transistor 76 andsupplies this voltage to a current sense input pin on the PFC IC 96. Inaddition to the pins referenced above, the PFC IC 96 also includes aground input pin that is connected to ground and a gate driver outputpin that is connected to the gate resistor 78 included with the PFCtransistor circuit 58.

The PFC IC 96 uses the voltage signals applied to its input pins togenerate a gate driver voltage that is supplied to the PFC transistor 76using the gate driver output pin on the PFC IC 96. The gate drivervoltage causes the PFC transistor 76 to switch off and on as indicatedpreviously. The PFC IC 96 is a conventional PFC IC, part number L6561,manufactured and sold by STMicroelectronics. Detailed informationregarding the internal structure and operation of this IC, as well assome of its associated circuitry discussed above, is described inApplication Notes AN966 and AN1089 and a document entitled “Power FactorCorrector” published by STMicroelectronics. Those documents are herebyincorporated by reference into this application.

The Voltage Regulator Circuit

As shown in FIG. 5, the PFC circuit 16 also includes a voltage regulatorcircuit 98 (the “regulator circuit 98”) that generates +5 and +15voltage reference voltages that can be used by the various ICs includedin the software dimming ballast 10. The regulator circuit 98 isconnected to the zero current detector circuit 92 as shown at terminal 7in FIG. 4 and FIG. 5 and generates the +5 and +15 volt referencevoltages based on a voltage generated across a capacitor 100 in thatcircuit. The regulator circuit 98 includes a regulator IC 102, aregulator input filter 104, a +5 volt output filter 106, and a +15 voltoutput filter 108.

The regulator IC 102 generates the +5 and +15 volt reference voltagesoutput by the regulator circuit 98. The regulator IC 102 used in thisembodiment is part number TLE 4484, manufactured and sold by Infineon.Detailed information regarding the internal structure and operation ofthis IC is described in a document entitled Dual Voltage Regulator with5 and 15 Volt Outputs, TLE 4484, published by Infineon. That document ishereby incorporated by reference into this application.

The regulator input filter 104 smoothes the voltage that is generated bythe zero current detector capacitor 100 and supplied to the regulatorcircuit 98 so that it is approximately constant, the +5 volt outputfilter 106 smoothes the +5 volt signal output by the regulator circuit98 so that it is approximately constant, and the +15 volt output filter108 smoothes the +15 volt signal output by the regulator circuit 98 sothat it is approximately constant. As shown in FIG. 5, the regulatorinput filter 104 is simply a capacitor 103, the +5 volt output filter106 is simply a pair of capacitors, 105 and 107, connected in parallel,and the +15 volt output filter 108 is simply a pair of capacitors, 109and 111, connected in parallel.

The Inverter Circuit

Referring to FIGS. 2 and 6, the inverter circuit 18 converts the boostedDC voltage supplied by the PFC circuit 16 into high frequency sinusoidalAC output voltages at terminals 7, 8 (the “AC output voltages”) and usesthese voltages to supply high frequency sinusoidal AC output currents(the “AC output currents”) to a fluorescent lamp 112 (the “lamp 112”).These voltages and currents are used to preheat, ignite, and vary thedimming level of the lamp 112.

To preheat that lamp 112, the inverter circuit 18 generates an AC outputvoltage and current having a frequency that is much higher than thenatural resonance frequency of a resonant output circuit included in theinverter circuit 18. The resonant output circuit is described in moredetail below. The magnitude of the AC output voltage generated by theinverter circuit 18 is relatively small compared to the magnitude of theboosted DC voltage supplied by the PFC circuit 16 and is insufficient toignite the lamp 112.

To ignite the lamp 112, the inverter circuit 118 generates an AC outputvoltage and current having a frequency that is approximately equal tothe natural resonance frequency of the resonant output circuit. Thisvoltage has a magnitude that is approximately equal to the magnitude ofthe boosted DC voltage supplied by the PFC circuit 16 and is sufficientto ignite the lamp 112.

To vary the dimming level of the lamp 112, the inverter circuit 18generates AC output voltages and currents having the same frequency butthat have varying magnitudes that depend on the desired dimming level ofthe lamp 112. Each one of these AC output voltages and currents has afrequency that is slightly higher than the natural resonance frequencyof the resonant output circuit.

To increase the dimming level of the lamp, the inverter circuit 18decreases the magnitude of the AC output current. This causes themagnitude of the AC output current supplied to the lamp 112 to decreaseand causes the lamp 112 to dim. In a similar manner, the invertercircuit 18 increases the magnitude of the AC output current in order todecrease the lamp dimming level. This causes the magnitude of the ACoutput current supplied to the lamp 112 to increase and causes the lamp112 to brighten.

The inverter circuit 18 generates the AC output voltages and currentsbased on inverter control signals received from the software controlledmicrocontroller circuit 22. The inverter control signals and thesoftware controlled micro controller 22 are described in more detailbelow.

The inverter circuit 18 includes an inverter input that receives theboosted DC voltage supplied by the PFC circuit 16 and an inverter outputthat can be used to supply the AC output voltage to the lamp 112. Theinverter circuit 18 also includes an inverter input filter 118, a halfbridge transistor switching circuit 120 (the “transistor switchingcircuit 120”), a half bridge transistor switching control circuit 122(the “switching control circuit 122”), and a series resonantinductor/capacitor (LC) output circuit (the “resonant output circuit124”).

The inverter input filter 118 filters high frequency noise generated bythe switching of the transistor switching circuit 120 and prevents itfrom passing back to the PFC circuit 16 and the AC power source 26. Asshown in FIG. 6, the inverter input filter 118 is simply a capacitor 118(the “inverter capacitor 118”) sized to pass DC voltage and to shortcircuit high frequency currents.

The transistor switching circuit 120 converts the boosted DC voltagesupplied by the PFC circuit 16 into high frequency pulsed AC voltageshaving magnitudes that vary from approximately zero to 450 volts,frequencies that range from being much higher, approximately equal to,and slightly higher than the natural resonance frequency of the resonantoutput circuit, and duty cycles that vary depending upon the desiredlamp dimming level. The pulsed AC voltage having a frequency much higherthan the natural resonant frequency of the resonant output circuitcauses the inverter circuit 18 to generate the AC voltage and currentnecessary to preheat the lamp 112. The pulsed AC voltage having afrequency that is approximately equal to the natural resonant frequencycauses the inverter circuit 18 to generate the AC voltage and currentnecessary to ignite the lamp 112. The pulsed AC voltages havingfrequencies that are slightly higher than the natural resonant frequencyof the resonant output circuit and varying duty cycles cause theinverter circuit 18 to generate the AC voltages and currents that varythe dimming level of the lamp 112.

The duty cycle of the pulsed AC voltages is defined as the ratio of thetime that the pulsed AC voltage is 450 volts over the time that thepulsed AC voltage is zero volts during a given period of the pulsed ACvoltage. In other words, the duty cycle represents the percentage oftime that the pulsed AC voltage is nonzero for a given period of thepulsed AC voltage.

The transistor switching circuit 120 generates pulsed AC voltages havingduty cycles ranging from approximately 20% for a maximum desired lampdimming level to approximately 96% for a minimum desired lamp dimminglevel.

As shown in FIG. 6, the transistor switching circuit 120 includes a highside power transistor 128 (the “HS transistor 128”), a high sidetransistor gate resistor 130 (the “HS gate resistor 130”), a high sidetransistor gate diode 132 (the “HS gate diode 132”), and a high sidetransistor blocking diode 134 (the “HS blocking diode 134”). Thetransistor switching circuit 120 also includes a low side powertransistor 136 (the “LS transistor 136”), a low side transistor gateresistor 138 (the “LS gate resistor 138”), a low side transistor gatediode 140 (the “LS gate diode 140”), and a low side transistor blockingdiode 142 (the “LS blocking diode 142”). The transistor switchingcircuit 120 further includes four free wheeling diodes, 144, 146, 148,and 150, connected as indicated in FIG. 6.

The HS gate resistor 130 limits gate current flowing into the gate ofthe HS transistor 128, the HS gate diode 132 allows gate current to flowout of the HS transistor 128 and bypass the HS gate resistor 130, andthe HS blocking diode 134 prevents current from flowing from theresonant output circuit 124, through the HS transistor 128, and to thePFC circuit 16.

The LS gate resistor 138, gate diode 140, and blocking diode 142 operatein a similar manner with respect to the LS transistor 136. The LS gateresistor 138 limits gate current flowing into the gate of the LStransistor 136, the LS gate diode 140 allows gate current to flow out ofthe LS transistor 136 and bypass the LS gate resistor 138, and the LSblocking diode 142 prevents current from flowing from the PFC circuit16, through the LS transistor 136, and into the resonant output circuit124.

The pulsed AC voltages are generated by simply switching the HS and LStransistors off and on in a manner that converts direct current suppliedby the PFC circuit 16 into alternating current. More specifically, thepulsed AC voltages are generated by alternating the switching of the HSand LS transistors. When the HS transistor 128 is on and the LStransistor 136 is off, direct current flows from the PFC circuit 16,through the HS transistor 128, and into the resonant output circuit 124.When the LS transistor 136 is on and the HS transistor 128 is off,direct current cannot flow from the PFC circuit 16 into the transistorswitching circuit 120. Instead, direct current flows in from theresonant output circuit 124 and through the LS transistor 136 to ground.

The four free wheeling diodes, 144, 146, 148, and 150, are used toconduct current when both transistors are turned off. The upper diodes,144 and 146, allow current to flow from the resonance output circuit 124back to the PFC circuit 16 when the HS transistor 128 has been switchedoff. Similarly, the lower diodes, 148 and 150, allow current to flowfrom the PFC circuit 16 into the resonant output circuit 124 when the LStransistor 136 has been switched off.

The switching control circuit 122 controls the transistor switchingcircuit 120 so that the duty cycle of the pulsed AC voltages ranges fromapproximately 20% to 96%. To perform this function, the switchingcontrol circuit 122 generates and outputs an internal HS control signal152 (see FIG. 6) that causes the HS transistor 128 to switch off and on,and generates and outputs an internal LS control signal 154 (see FIG. 6)that causes the LS transistor 136 to switch off and on.

The internal HS and LS control signals are generated by the switchingcontrol circuit 122 based on inverter HS and LS control signals, 156 and158, respectively, received from the software controlled microcontrollercircuit 22 (see FIGS. 2 and 8) included with this embodiment of thepresent invention. The software controlled microcontroller circuit 22 isdiscussed in more detail below. The internal HS and LS control signalsare pulse width modulated control signals. In a similar manner, theinverter HS and LS control signals are pulse width modulated controlsignals. The primary difference between the internal and invertercontrol signals is that the internal control signals are suitable fordriving the HS and LS transistors in the transistor switching circuit120 and the inverter control signals are not.

By varying the pulse widths of the inverter HS and LS control signals,the duty cycle of the pulsed AC voltages can be varied. If the pulsewidth is increased, the duty cycle increases. If the pulse width isdecreased, the duty cycle decreases.

As shown in FIG. 6, the switching control circuit 122 includes aninverter IC 122 (the “inverter IC 122”) having a high side transistordrive input pin (the “HS drive input”), a low side transistor driveinput pin (the “LS drive input”), an inverter supply voltage input pin(the “inverter supply input”), an inverter ground pin, a low sidetransistor drive output pin (the “LS drive output”), an inverterfloating reference voltage output pin (the “inverter reference output”),a high side transistor drive output pin (the “HS drive output”), and abootstrap supply voltage input pin (the “bootstrap supply input”). It isthis circuit component that receives the inverter HS and LS controlsignals and outputs the internal HS and LS control signals. The inverterIC 122 is a conventional inverter IC, part number L6387, manufacturedand sold by STMicroelectronics. Detailed information regarding thestructure and operation of this IC is described in Application NoteAN994 published by STMicroelectronics. That document is herebyincorporated by reference into this application.

The resonant output circuit 124 filters the pulsed AC voltages generatedby the transistor switching circuit 120 to generate the AC outputvoltages that are supplied to the lamp 112. For the pulsed AC voltagehaving a frequency that is much higher than the natural resonancefrequency of the resonant output circuit 124, the output circuit 124converts the pulsed AC voltage into a sinusoidal AC voltage having amagnitude that is relatively small compared to the magnitude of thepulsed AC voltage. For the pulsed AC voltage having a frequency that isapproximately equal to the natural resonance frequency, the outputcircuit 124 converts the pulsed AC voltage into a sinusoidal AC voltagehaving a magnitude that is approximately equal to the magnitude of thepulsed AC voltage.

For the pulsed AC voltages having frequencies that are slightly higherthan the natural resonance frequency and varying duty cycles, the outputcircuit 124 converts these voltages into sinusoidal AC voltages havingmagnitudes that vary depending upon the duty cycles of these pulsed ACvoltages. For a pulsed AC voltage having a 96% duty cycle, the magnitudeof the ac output current corresponds to full brightness. For a pulsed ACvoltage having approximately 20% duty cycle, the magnitude of the ACoutput current corresponds to full dim.

As indicated in FIG. 6, the resonant output circuit 124 includes threeinductors connected in series, 160, 162, and 164, with a singlecapacitor 166. In addition, the resonant output circuit 124 includes alamp filament warming and current limiting circuit 168 made up of aseries of resistors, capacitors, and inductors. The three inductors,160, 162, and 164, and the capacitor 166 perform the filtering of thesquare wave AC voltage 126 and cause the AC output voltage 110 to appearacross the capacitor 166. The capacitor and inductors in the lampfilament warming and current limiting circuit 168 limit current flowingin the lamp 112 and the inductors are used to warm lamp filaments priorto lamp ignition.

The inverter circuit 18 also includes a half bridge DC blockingcapacitor 170 that is used to sense end of lamp life fault conditions asdescribed in more detail below, i.e. positive DC rectification, negativeDC rectification, or symmetric high voltage conditions.

The Software Controlled Microcontroller Circuit 22

The software controlled microcontroller circuit 22 (the “microcontrollercircuit 22”) is connected to the PFC circuit 16, inverter circuit 18,and the lamp dimming level feedback signal conditioning circuit 20 asshown in FIG. 7 and is designed to perform a variety of differentfunctions.

The microcontroller circuit 22 is designed to generate inverter controlsignals that cause the inverter circuit 18 to supply the lamp 112 withappropriate voltages and currents for preheating, striking, and varyingthe dimming level of the lamp 112. The microcontroller circuit 22 isdesigned to monitor the AC input voltage supplied to the softwaredimming ballast 10 and to shut down the ballast if that voltage fallsbelow a level that can be used by the inverter circuit 18 to supply therequired voltages and currents to the lamp 112. The microcontrollercircuit 22 is also designed to monitor the operating condition of thelamp 112 and, when the lamp 112 reaches an end of lamp life condition,to shut down the software dimming ballast 10. The microcontrollercircuit 22 is further designed to control the dimming level of the lamp112 based on analog or digital dimming control signals representative ofa desired lamp dimming level and a lamp dimming level feedback signalrepresentative of an existing lamp dimming level.

The microcontroller circuit 22 implements its various functions using amicrocontroller IC and control software loaded on that IC, both of whichare discussed in more detail below.

The Microcontroller IC

Referring now to FIG. 8, the microcontroller circuit 22 includes amicrocontroller IC 172 that is used to generate the inverter HS and LScontrol signals, 156 and 158, that are supplied to the switching controlcircuit 122 in the inverter circuit 18, and control software (not shown)that is used to cause the microcontroller IC 172 to generate thosecontrol signals.

The microcontroller IC 172 includes an analog dimming control signalinput (the “analog dimming input”), a digital dimming control signalinput (the “digital dimming input”), a lamp dimming level feedbacksignal input (the “lamp feedback input”), a line voltage feedback signalinput (the “line feedback input”), a DC blocking capacitor feedbacksignal input (the “blocking capacitor feedback input”), amicrocontroller HS transistor control signal output (the“microcontroller HS control output”), and a microcontroller LStransistor control signal output (the “microcontroller LS controloutput”).

The microcontroller IC 172 shown in FIG. 8 is part number ATmega8,manufactured and sold by Atmel Corporation. The operation andcapabilities of this IC are described in a document entitled “8-bit AVRwith 8K Bytes In-System Programmable Flash” published by Atmel. Thatdocument is hereby incorporated by reference into this application.

The analog dimming input is designed to receive an analog DC voltagedimming control signal representative of a desired lamp dimming level174 (the “analog dimming control signal 174”). The analog dimmingcontrol signal 174 may have a value ranging from 0-5 volts DC, with 0volts representing a maximum lamp dimming level and 5 volts representinga minimum dimming level. This signal is used by the microcontrollercircuit 22 to determine the desired dimming level for the lamp 112.

In a similar manner, the digital dimming input is designed to receive adigital dimming control signal 176 representative of a desired lampdimming level. The digital dimming control signal 176 includes digitalcodes representing lamp dimming levels ranging from a minimum lampdimming level to a maximum lamp dimming level. As was the case with theanalog dimming control signal 174, the microcontroller circuit 22 usesthe digital dimming control signal 176 to determine the desired dimminglevel for the lamp 112.

The lamp feedback input is connected to a lamp dimming level feedbacksignal conditioning circuit 20 (see FIGS. 2 and 9), which is describedin more detail below, and is designed to receive an analog DC voltagefeedback signal 178 representative of an existing lamp dimming levelgenerated by that circuit (the “lamp dimming level feedback signal178”). The lamp dimming level feedback signal 178 may have a valueranging from 0-5 volts DC, with 0 volts representing a maximum existingdimming level and 5 volts representing a minimum existing dimming level.The microcontroller circuit 22 uses this feedback signal to determinethe existing lamp dimming level.

The line feedback input is connected to the PFC circuit 16 through aline voltage signal conditioning circuit 180 (see FIG. 8) and isdesigned to receive a rectified AC voltage 182 that is proportional tothe rectified AC voltage generated by the AC/DC converter circuit 14 andconditioned by the line voltage signal conditioning circuit 180 (the“line feedback signal 182”). The line feedback signal 182 may have avalue ranging from 0-5 volts DC, with 0 volts representing a minimumline voltage and 5 volts representing a maximum line voltage. Themicrocontroller circuit 22 uses this feedback signal to monitor the ACinput voltage 28 supplied by the AC power source 26 and, if it drops toolow, shuts down the software dimming ballast 10.

The blocking capacitor feedback input is connected to the half bridge DCblocking capacitor 170 (the “blocking capacitor 170”) through a blockingcapacitor signal conditioning circuit 184 (see FIG. 8) and is designedto receive a DC voltage 186 that develops on the blocking capacitor 170(the “blocking capacitor feedback signal 186”) and is conditioned by theblocking capacitor signal conditioning circuit 184. The blockingcapacitor feedback signal 186 may have a value ranging from 0-5 voltsDC. The microcontroller circuit 22 uses this feedback signal to monitorthe condition of the lamp 112 and to detect end of lamp life faultconditions. If an end of lamp life condition occurs, the microcontrollercircuit 22 shuts down the software dimming ballast 10.

The microcontroller IC 172 converts the analog dimming control signal174, the lamp dimming level feedback signal 178, the line feedbacksignal 182, and the blocking capacitor feedback signal 186 into digitaldata. The analog dimming control signal 174 is converted into digitaldata that is representative of the desired lamp dimming level associatedwith the analog dimming control signal (the “desired dimming leveldigital data”) and the lamp dimming level feedback signal 178 isconverted into digital data representative of the existing lamp dimminglevel associated with the lamp dimming level feedback signal (the“existing dimming level digital data”). In a similar manner, the linefeedback signal 182 is converted into digital data representative of theline voltage associated with the line feedback signal (the “line voltagedigital data”) and the blocking capacitor feedback signal 186 isconverted into digital data representative of the blocking capacitorvoltage associated with the blocking capacitor feedback signal (the“blocking capacitor digital data”).

The inverter HS control output is connected to the HS drive input on theswitching control circuit 122 in the inverter circuit 18 and is used tosupply the switching control circuit 122 with the microcontroller HScontrol signal discussed previously.

The microcontroller LS drive output is connected to the LS drive inputon the switching control circuit 122 in the inverter circuit 18 and isused to supply the switching control circuit 122 with the inverter LScontrol signal discussed previously.

The Control Software

The applicant of the present application has developed three differentversions of the control software (the “software”) that can be loaded onthe microcontroller IC 172 and used to control lamp preheating,striking, and dimming. The first, the analog control software, isdesigned to be used when lamp dimming is controlled using the analogdimming control signal. The second, the digital control software, isdesigned to be used when lamp dimming is controlled using the digitaldimming control signal. And, the third, the combination controlsoftware, is designed to be used when lamp dimming is controlled usingeither an analog dimming control signal or a digital dimming controlsignal. The preheating and striking code used in each version of thesoftware is the same.

The analog control software (the “analog software”) is designed to causethe microcontroller IC 172 to compare the desired dimming level digitaldata 188 and the existing dimming level digital data 190 to determine ifthe lamp 112 is at the desired lamp dimming level. If not, the analogsoftware causes the microcontroller IC 172 to change the duty cycle,i.e., the pulse width, of the inverter HS and LS pulse width modulatedcontrol signals until the lamp 112 reaches the desired lamp dimminglevel.

If the existing lamp dimming level is higher than the desired lampdimming level, i.e., the existing lamp light output is dimmer thandesired, the pulse width is increased and the lamp light outputincreases. Conversely, if the existing lamp dimming level is lower thandesired, i.e., the existing lamp light output is brighter than desired,the pulse width is decreased and the lamp light output decreases.

The analog software is also designed to read the line voltage digitaldata and the blocking capacitor digital data and to store this data inthe microcontroller IC 712. The analog software compares the linevoltage digital data to digital data stored in the microcontrollermemory that is representative of a minimum line voltage that can beapplied to the software dimming ballast 10 and that allows the invertercircuit 18 to operate properly (the “minimum line voltage data”). If thecomparison indicates that the line voltage is below the minimum linevoltage, the analog software causes the microcontroller IC 172 to shutdown the software dimming ballast 10.

The analog software compares the blocking capacitor digital data todigital data stored in the microcontroller IC 172 that is representativeof a DC end of lamp life voltage on the blocking capacitor 170 thatindicates the lamp 112 has reached an end of lamp life condition (the“end of lamp life data”). If the comparison indicates that the voltageon the blocking capacitor 170 is equal to the end of lamp life voltage,the analog software causes the microcontroller IC 172 to shut down thesoftware dimming ballast 10.

The digital software operates in a similar manner. The digital softwareis designed to read the digital data applied to the digital dimminginput and the existing dimming level digital data generated by themicrocontroller IC 172 and to store that data in the microcontroller IC172. The digital software then processes the desired dimming leveldigital data and the existing dimming level digital data in the samemanner as the analog software discussed above.

The combination software includes code that allows it to determine if ananalog dimming control signal or a digital dimming control signal hasbeen applied to the microcontroller IC 172. If an analog dimming controlsignal is applied, the combination software operates in the same manneras the analog software described previously. If a digital dimmingcontrol signal is applied, the combination software operates in the samemanner as the digital software discussed above. If both types of dimmingcontrol signals are applied, the combination software defaults to usingthe digital dimming control signal to control lamp dimming.

The Lamp Dimming Level Feedback Signal Conditioning Circuit 20

Referring to FIG. 9, the lamp dimming level feedback signal conditioningcircuit 20 (the “feedback signal conditioning circuit 20”) is designedto be connected to the inverter circuit 18, to receive an AC lampcurrent feedback signal from the inverter circuit 18 that isproportional to AC current flowing through the lamp 112, and to convertthat AC lamp current feedback signal into the analog DC voltage feedbacksignal 178 that is supplied to the microcontroller circuit 22. Morespecifically, the feedback signal conditioning circuit 20 converts theAC lamp current feedback signal into an AC voltage signal, limits thatAC voltage signal to a predetermined AC voltage level to generate alimited AC voltage, rectifies that limited AC voltage to generate arectified DC voltage, filters that rectified DC voltage to obtain afiltered DC voltage, amplifies the filtered DC voltage to generate anamplified DC voltage, rectifies the amplified DC voltage to eliminatenegative going transients, and filters the rectified and amplified DCvoltage to generate the analog DC voltage feedback signal 178.

To implement these functions, the feedback signal conditioning circuit20 includes a voltage generating circuit 210, an amplifying circuit 212connected to the voltage generating circuit 210, a rectifying circuit214 connected to the amplifying circuit 212, and an output filtercircuit 216 connected to the rectifying circuit 214.

As shown in FIG. 9, the voltage generating circuit 210 includes a pairof resistors, 218 and 220, connected in parallel with one another and aZener diode 222 connected in parallel with the resistors. The resistors,218 and 220, convert AC lamp current from the inverter circuit 18 intoAC voltage, and the Zener diode 222 rectifies the AC voltage to generatea DC voltage and limits the DC voltage to the breakdown voltage of theZener diode 222.

To reduce the amount of power dissipated, the resistors, 218 and 220,are sized so that they have as little resistance as possible and arestill able to generate an AC voltage suitable for use by the amplifyingcircuit 212. In addition, the breakdown voltage of the Zener diode 222is selected so that the DC voltage applied to the amplifying circuit 212does not exceed the input voltage limitations of that circuit.

The amplifying circuit 212 includes an operational amplifier 224, anamplifier input filter 226, and an amplifier gain circuit 228. In FIG.9, the operational amplifier 224 is a conventional operational amplifierand includes an inverting input, a noninverting input, and an amplifieroutput. In combination with the amplifier gain circuit 228, theoperational amplifier 224 amplifies the DC voltage signal generated bythe voltage generating circuit 210 so that it can be applied to themicrocontroller circuit 22.

The amplifier gain circuit 228 includes a gain resistor 232 and gaincapacitor 234 connected in parallel with one another and connected tothe inverting input and the output of the amplifier 224. These twocomponents determine, in part, the gain of the operational amplifier224. Amplifier gain is also determined, in part, by a second gainresistor 234 connected to the inverting and noninverting inputs of theoperational amplifier 224 as shown in FIG. 9.

The amplifier input filter 226 is connected to the inverting input ofthe operational amplifier 224 and is a low pass input filter designed tofilter out high frequency noise that may be present in the DC voltagegenerated by the voltage generating circuit 210. The amplifier inputfilter 226 includes an input filter resistor 236 connected to an inputfilter capacitor 238.

The rectifying circuit 214 shown in FIG. 9 is a conventional diode 214that simply rectifies the output of the amplifying circuit 212 togenerate a rectified DC voltage. The output filter circuit 216 is a lowpass filter circuit designed to filter out high frequency noise that maybe present in the rectified DC voltage generated by the rectifyingcircuit 214 and includes an output filter resistor 240 connected inseries with an output filter capacitor 242. The output filter circuit216 also includes a second output filter resistor 244 that is used todischarge the output filter capacitor 242 when the voltage applied tothe output filter circuit 216 drops to zero.

Alternative Embodiments of the Present Invention

The software dimming ballast 10 of the present invention may vary in anumber of different ways. For example, the software dimming ballast 10as described above may be connected to a DC power source rather than theAC power source 26. Alternatively, the converter circuit 14 and the PFCcircuit 16 in the above-referenced embodiment can be eliminated entirelyand this modified version of the software dimming ballast 10 can beconnected to the DC power source.

The 60 Hz AC power source 26 may be replaced with a 50 Hz AC powersource in another embodiment. In that embodiment, the various circuitcomponents included in the software dimming ballast 10 are designed toreceive 50 Hz AC power rather than 60 Hz AC power.

In other embodiments, the EMI filter and the PFC circuits may both beexcluded from the software dimming ballast 10 of the present invention.This is true regardless of whether an AC power source or a DC powersource is to be connected to the software dimming ballast 10. If thereis very little noise present in the software dimming ballast 10, or thenoise is at a tolerable level for a certain application, the EMI filtercircuit 12 may be excluded. Also, if power factor correction is not anissue and the DC power generated by the converter circuit 14 or a DCpower source is sufficiently high, the PFC circuit may be excluded.

In still other embodiments, a variety of different types of EMI filterand PFC circuits may be used with the present invention. The prior artincludes EMI filter circuits that have different filtering capabilitiesand any one of these filters may be used with embodiments of the presentinvention.

Similarly, the prior art includes a variety of different types of PFCcircuits. For example, the prior art includes PFC circuits that providepower factors that are less than 0.95. In addition, the prior artincludes PFC circuits that do not generate a boosted DC voltage at allor generate a boosted DC voltage that has a magnitude that is less than450 volts. Other PFC circuits use different PFC ICs and have switchingfrequencies that are higher or lower than the 10-15 kHz switchingfrequency discussed above. Any one of these PFC circuits may be used inembodiments of the present invention.

AC/DC converter circuits are well known in the art and any one of avariety of different types of converters may be used in embodiments ofthe present invention. For example, the prior art includes single diodeconverters and half-bridge converters. Embodiments of the presentinvention may include either of these types of converters. Still otherembodiments may include regulator circuits that include differentregulator ICs.

The inverter circuit 18 used in the present invention may also vary. Forexample, the inverter circuit 18 may include a full bridge transistorswitching circuit or a push pull transistor switching circuit. Inaddition, the inverter circuit 18 may include a parallel resonant LCoutput circuit rather than the series resonant LC output circuitdiscussed above. The inverter circuit 18 may use BJT or MOSFET powertransistors.

The inverter circuit 18 may output AC output voltages having a varietyof different frequencies in order to preheat and strike the lamp 112.The magnitude of the AC output voltages may be higher or lower than the450 volt AC output voltage discussed previously. The inverter circuit 18may include different inverter ICs, different microcontroller ICs, orboth. The control software may be designed to cause the microcontrollerIC 172 to vary the frequency of the pulse width modulated invertercontrol signals in order to control lamp dimming rather than varying theduty cycle of the inverter control signals. The control software mayalso be designed to generate inverter control signals having varyingduty cycles and frequencies in order to control lamp dimming.

The control software may be modified so that it does not process theline voltage and HB capacitor feedback signals and shut down thesoftware dimming ballast 10 when these signals indicate that the linevoltage is too low or the lamp 112 has reached an end of lamp lifecondition. The microcontroller IC 172 may be designed to receive andprocess digital dimming control signals that have a variety of differentdigital protocols. The software dimming ballast 10 may also include ananalog dimming signal conditioning circuit 20 that can be used toconvert a 0-10 volt analog dimming control signal generated by aconventional 0-10 volt dimming control device into a 0-5 volt analogdimming control signal required by the microcontroller IC.

The feedback signal conditioning circuit 20 may also vary from oneembodiment to another. For example, the feedback signal conditioningcircuit 20 may be modified so that it does not limit the AC voltagegenerated by this circuit, filter the rectified DC voltage generated bythis circuit, amplify the filtered DC voltage generated by this circuit,rectify the amplified DC voltage signal generated by this circuit, or sothat it does not filter the rectified and amplified DC voltage signalgenerated by this circuit. In addition, the amplifier gain circuit maybe modified so that it can be adjusted by the control software so thatthe gain of the amplifier is dependent upon the magnitude of therectified DC voltage applied to the amplifier. If the DC voltage dropsdown to a predetermined level, the gain can be increased. In a similarmanner, if the DC voltage increases to a predetermined level, the gaincan be decreased.

Thus, although there have been described particular embodiments of thepresent invention of a new and useful Software Controlled ElectronicDimming Ballast, it is not intended that such references be construed aslimitations upon the scope of this invention except as set forth in thefollowing claims.

1. A software controlled electronic dimming ballast, comprising; aninverter circuit for supplying current to a lamp: a dimming controlcircuit for controlling the current supplied by the inverter circuit tothe lamp and thereby causing the lamp to have a desired lamp dimminglevel, the dimming control circuit including a dimming control signalinput for receiving a dimming control signal representative of thedesired lamp dimming level, a lamp dimming level feedback signal inputfor receiving a lamp dimming level feedback signal representative of anexisting lamp dimming level, and an inverter control signal output foroutputting an inverter control signal that causes the inverter circuitto supply the lamp with sufficient current to cause the lamp to have thedesired lamp dimming level; the dimming control circuit furtherincluding lamp dimming level control software for causing the dimmingcontrol circuit to generate the inverter control signal based on thedimming control signal and the lamp dimming level feedback signal; thedimming control circuit still further including a lamp dimming levelfeedback signal conditioning circuit for generating the lamp dimminglevel feedback signal; wherein the lamp dimming level feedback signalconditioning circuit includes a voltage generating circuit forgenerating a voltage signal representative of the existing lamp dimminglevel based on a lamp current signal representative of the existing lampdimming level; and wherein the voltage signal is the lamp dimming levelfeedback signal.
 2. The dimming ballast of claim 1, wherein the voltagegenerating circuit includes a resistor.
 3. The dimming ballast of claim2, wherein the voltage generating circuit further includes a diodeconnected in parallel with the resistor.
 4. The dimming ballast of claim2, wherein the voltage generating circuit further includes a Zener diodeconnected in parallel with the resistor.
 5. The dimming ballast of claim1, wherein the voltage generating circuit includes a capacitor.
 6. Thedimming ballast of claim 5, wherein the voltage generating circuitfurther includes a diode connected in parallel with the capacitor. 7.The dimming ballast of claim 5, wherein the voltage generating circuitfurther includes a Zener diode connected in parallel with the capacitor.8. The dimming ballast of claim 7, wherein the voltage generatingcircuit further includes a diode connected in parallel with theresistor.
 9. The dimming ballast of claim 1, wherein the voltagegenerating circuit includes a capacitor connected in series with aresistor.
 10. The dimming ballast of claim 9, wherein the voltagegenerating circuit further includes a Zener diode connected in parallelwith the resistor.
 11. The dimming ballast of claim 1, wherein thevoltage generating circuit includes a current transformer.
 12. Thedimming ballast of claim 1, wherein the lamp dimming level feedbacksignal conditioning circuit includes: an amplifying circuit foramplifying the voltage signal generated by the voltage generatingcircuit for use as the lamp dimming level feedback signal.
 13. Thedimming ballast of claim 12, wherein: the amplifying circuit includes aninput filter circuit for generating a filtered voltage signal byfiltering the voltage signal generated by the voltage generatingcircuit; and the amplifying circuit amplifies the filtered voltagesignal.
 14. The dimming ballast of claim 12, wherein the amplifyingcircuit includes an operational amplifier for amplifying the filteredvoltage signal.
 15. The dimming ballast of claim 12, wherein theamplifying circuit includes an amplifier gain circuit for controllingamplifier gain.
 16. The dimming ballast of claim 12, wherein theamplifying circuit includes an adjustable amplifier gain circuit forvarying amplifier gain based on the dimming control signal.
 17. Thedimming ballast of claim 1, wherein the lamp dimming level feedbacksignal conditioning circuit includes: an amplifying circuit foramplifying the voltage signal generated by the voltage generatingcircuit; a rectifying circuit for generating a rectified voltage signalrepresentative of the existing lamp dimming level by rectifying thevoltage signal amplified by the amplifying circuit for use as the lampdimming level feedback signal.
 18. The dimming ballast of claim 17,wherein the rectifying circuit includes a diode.
 19. The dimming ballastof claim 1, wherein the lamp dimming level feedback signal conditioningcircuit includes: an amplifying circuit for amplifying the voltagesignal generated by the voltage generating circuit; a rectifying circuitfor rectifying the voltage signal amplified by the amplifying circuit;an output filter circuit for filtering the voltage signal rectified bythe rectifying circuit for use as the lamp dimming level feedbacksignal.
 20. The dimming ballast of claim 19, wherein the output filtercircuit includes: an output filter resistor connected in series with anoutput filter capacitor; and a discharge resistor connected in parallelwith the output filter resistor and output filter capacitor.
 21. Asoftware controlled electronic dimming ballast, comprising: an invertercircuit for supplying current to a lamp; a dimming control circuit forcontrolling the current supplied by the inverter circuit to the lamp andthereby causing the lamp to have a desired lamp dimming level, thedimming control circuit including a microcontroller integrated circuit(IC) for generating an inverter control signal that causes the invertercircuit to supply the lamp with sufficient current to cause the lamp tohave the desired lamp dimming level and a lamp dimming level feedbacksignal conditioning circuit for generating a lamp dimming level feedbacksignal representative of an existing lamp dimming level, themicrocontroller IC including a dimming control signal input forreceiving a dimming control signal representative of the desired lampdimming level, a lamp dimming level feedback signal input for receivingthe lamp dimming level feedback signal, an inverter control signaloutput for outputting the inverter control signal, and lamp dimminglevel control software for causing the microcontroller IC to generatethe inverter control signal based on the dimming control signal and thelamp dimming level feedback signal; the microcontroller IC converts thedimming control signal into desired dimming level digital datarepresentative of the desired lamp dimming level; the microcontroller ICconverts the lamp dimming level feedback signal into existing lampdimming level digital data representative of the existing lamp dimminglevel; the lamp dimming level control software causes themicrocontroller IC to generate the inverter control signal based on thedesired dimming level digital data and the existing lamp dimming leveldigital data; and wherein the lamp dimming level feedback signalconditioning circuit includes a voltage generating circuit forgenerating a voltage signal representative of the existing lamp dimminglevel based on a lamp current signal representative of the existing lampdimming level; an amplifying circuit for generating an amplified voltagesignal representative of the existing lamp dimming level by amplifyingthe voltage signal generated by the voltage generating circuit; andwherein the amplified voltage signal is the lamp dimming level feedbacksignal.
 22. The dimming ballast of claim 21, further comprising: analternating current/direct current (AC/DC) converter circuit forconverting low frequency AC voltage into DC voltage and for supplyingthe DC voltage to the inverter circuit; and wherein the inverter circuitconverts the DC voltage into high frequency AC voltage and uses the highfrequency AC voltage to supply current to the lamp.
 23. The dimmingballast of claim 22, further comprising an electromagnetic interference(EMI) filter circuit for filtering EMI out of the low frequency ACvoltage converted by the AC/DC converter circuit.
 24. The dimmingballast of claim 21, further comprising: an alternating current/directcurrent (AC/DC) converter circuit for converting low frequency ACvoltage into DC voltage; a power factor correction (PFC) circuit forgenerating a boosted DC voltage by boosting the DC voltage generated bythe AC/DC converter circuit, for supplying the boosted DC voltage to theinverter circuit, and for causing power drawn by the dimming ballast tohave a desired power factor; and wherein the inverter circuit convertsthe boosted DC voltage into high frequency AC voltage and uses the highfrequency AC voltage to supply current to the lamp.
 25. The dimmingballast of claim 24, further comprising an EMI filter circuit forfiltering EMI out of the low frequency AC voltage converted by the AC/DCconverter circuit.